Hooks supports two directories, process default and override

ALso cleanup files section or podman man page

Add description of policy.json
Sort alphabetically.
Add more info on  oci hooks

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Closes: #1487
Approved by: umohnani8
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f